Fix Singletons and Singleton Spawn

 * Fixes open-mpi#10590
 * Singletons will not have a PMIx value for `PMIX_LOCAL_PEERS`
   so make that optional instead of required.
 * `&` is being confused as an application argument in `prte`
   instead of the background character
   * Replace with `--daemonize` which is probably better anyway

Signed-off-by: Joshua Hursey <jhursey@us.ibm.com>

ompi/dpm/dpm.c

@@ -23,6 +23,7 @@
  * Copyright (c) 2021      Nanook Consulting.  All rights reserved.
  * Copyright (c) 2018-2022 Triad National Security, LLC. All rights
  *                         reserved.
+ * Copyright (c) 2022      IBM Corporation.  All rights reserved.
  * $COPYRIGHT$
  *
  * Additional copyrights may follow
@@ -2042,7 +2043,7 @@ static int start_dvm(char **hostfiles, char **dash_host)
     opal_asprintf(&tmp, "%d", death_pipe[0]);
     opal_argv_append_nosize(&args, tmp);
     free(tmp);
-    opal_argv_append_nosize(&args, "&");
+    opal_argv_append_nosize(&args, "--daemonize");
 
     /* Fork off the child */
     pid = fork();

ompi/runtime/ompi_rte.c

@@ -15,7 +15,7 @@
  * Copyright (c) 2020      Amazon.com, Inc. or its affiliates.  All Rights
  *                         reserved.
  * Copyright (c) 2021      Nanook Consulting.  All rights reserved.
- * Copyright (c) 2021      IBM Corporation. All rights reserved.
+ * Copyright (c) 2021-2022 IBM Corporation.  All rights reserved.
  * $COPYRIGHT$
  */
 #include "ompi_config.h"
@@ -848,19 +848,21 @@ int ompi_rte_init(int *pargc, char ***pargv)
 
     /* retrieve the local peers - defaults to local node */
     val = NULL;
-    OPAL_MODEX_RECV_VALUE(rc, PMIX_LOCAL_PEERS,
-                          &pname, &val, PMIX_STRING);
+    OPAL_MODEX_RECV_VALUE_OPTIONAL(rc, PMIX_LOCAL_PEERS,
+                                   &pname, &val, PMIX_STRING);
     if (PMIX_SUCCESS == rc && NULL != val) {
         peers = opal_argv_split(val, ',');
         free(val);
     } else {
-        ret = opal_pmix_convert_status(rc);
-        error = "local peers";
-        goto error;
+        peers = NULL;
     }
     /* if we were unable to retrieve the #local peers, set it here */
     if (0 == opal_process_info.num_local_peers) {
-        opal_process_info.num_local_peers = opal_argv_count(peers) - 1;
+        if (NULL != peers) {
+            opal_process_info.num_local_peers = opal_argv_count(peers) - 1;
+        } else {
+            opal_process_info.num_local_peers = 1;
+        }
     }
     /* if my local rank if too high, then that's an error */
     if (opal_process_info.num_local_peers < opal_process_info.my_local_rank) {